1. Field of the Invention
The present invention is generally related to a cooling system for a four cycle engine and, more particularly, to a cooling system that connects the cooling cavities of the cylinder head, exhaust conduit, and cylinder block of the engine in series fluid communication with each other in a manner which conducts the cooling water through the cylinder block only after the cooling water has passed through the cylinder head and the exhaust conduit.
2. Description of the Prior Art
Many types of cooling systems are well known to those skilled in the art for removing heat from an internal combustion engine used in conjunction with a marine propulsion system.
U.S. Pat. No. 5,937,802, which issued to Bethel et al on Aug. 17, 1999, discloses an engine cooling system for an internal combustion engine which is provided with coolant paths through the cylinder block and cylinder head which are connected in serial fluid communication with each other. In parallel with the cooling path through the cylinder head, a first drain is connected in serial fluid communication with a pressure responsive valve and the path through the cylinder block. A temperature responsive valve is connected in serial fluid communication with the cylinder head path and in parallel fluid communication with the first drain. A pump is provided to induce fluid flow through the first and second coolant conduits and the first and second drains, depending on the state of the pressure responsive valve and the temperature responsive valve.
U.S. Pat. No. 6,068,529, which issued to Weronke et al on May 30, 2000, discloses a water propulsion unit with dual water inlet structure. A vertical drive shaft is journaled in the lower gearcase and drives a pair of bevel gears. The propulsion unit includes a dual cooling water pick-up system in which seawater is drawn to the water pump both through a series of vertical inlet ports in the gearcase and through a plurality of inlet holes that are located in the forward end of the lower torpedo section.
U.S. Pat. No. 5,937,801, which issued to Davis on Aug. 17, 1999, discloses an oil temperature moderator for an internal combustion engine. A cooling system is provided for an outboard motor or other marine propulsion system which causes cooling water to flow in intimate thermal communication with the oil pan of the engine by providing a controlled volume of cooling water at the downstream portion of the water path. As cooling water flows from the outlet of the internal combustion engine, it is caused to pass in thermal communication with the oil pan. Certain embodiments also provide a pressure activated valve which restricts the flow from the outlet of the internal combustion engine to the space near the oil pan. One embodiment of the cooling system also provides a darn within the space adjacent to the outer surface of the oil pan to divide that space into first and second portions. The dam further slows the flow of water as it passes in thermal communication with the oil pan.
U.S. Pat. No. 5,383,803, which issued to Pilgrim on Jan. 24, 1995, describes an outboard motor cooling system. An outboard motor is equipped with a closed circuit cooling system having a coolant pump, a heat exchanger, an expansion tank, a series of coolant passage in the motor and some external piping to complete the circuit. In one embodiment of the invention, a conventional outboard motor is modified to include the closed circuit coolant system with the conventional water pump being converted to the coolant pump. In this modified embodiment, the thermostat seals have to be modified, the pump has to be sealed, and several bypass holes have to be plugged in the engine to isolate the flow of the coolant.
U.S. Pat. No. 6,295,963, which issued to Kollock et al on Oct. 2, 2001, discloses a four cycle engine for marine propulsion system. A marine engine is made with a head portion that includes an exhaust manifold that is formed as an integral part of the head portion during a lost foam casting procedure. The head portion comprises a plurality of combustion chambers in which each combustion chamber has at least one exhaust throat that connects the combustion chamber in fluid communication with at least one exhaust port. All of the exhaust ports connect associated combustion chambers in fluid communication with an exhaust manifold that is formed integrally within the head portion during the initial lost foam casting process. An exhaust outlet opening from the exhaust manifold is positioned above at least one exhaust port of at least one combustion chamber to form a water trap or stand pipe that inhibits water ingestion under certain adverse conditions. Water passages and oil passages are formed integrally within the head portion during the lost foam casting process. The head portion of the present invention reduces the number of components needed to provide the functions of the cylinder head portion and, as a result, improves reliability and reduces cost.
U.S. Pat. No. 6,405,692, which issued to Christiansen on Jun. 18, 2002, discloses an outboard motor with a screw compressor supercharger. The outboard motor has a screw compressor which provides a pressurized charge for the combustion chambers of the engine. The screw compressor has first and second screw rotors arranged to rotate about vertical axes which are parallel to the axes of a crankshaft of the engine. A bypass valve regulates the flow of air through a bypass conduit extending from an outlet passage of the screw compressor to the inlet passage of the screw compressor. A charge air cooler is used in a preferred embodiment and the bypass conduit then extends between the cold side plenum of the charge air cooler and the inlet of the compressor. The bypass valve is controlled by an engine control module in order to improve power output from the engine at low engine speeds while avoiding any violation of existing limits on the power of the engine at higher engine speeds.
U.S. Pat. No. 6,408,832, which issued to Christiansen on Jun. 25, 2002, discloses an outboard motor with a charge air cooler. An outboard motor is provided with an engine having a screw compressor which provides a pressurized charge for the combustion chambers of the engine. A charge air cooler is used in a preferred embodiment and the bypass conduit of the screw compressor then extends between the cold side plenum of the charge air cooler and the inlet of the compressor. The charge air cooler improves the operating efficiency of the engine and avoids overheating the air as it passes through the supercharger after flowing through a bypass conduit. The bypass valve is controlled by an engine control module in order to improve power output from the engine at low engine speeds while avoiding any violation of existing limits on the power of the engine at higher engine speeds.
U.S. Pat. No. 5,522,351, which issued to Hudson on Jun. 4, 1996, discloses an internal combustion engine temperature control system. The invention is a liquid to liquid heat exchanger incorporated into the body of an internal combustion engine. The first cooling liquid (e.g. oil) is circulated through passages in the engine block and along one side of a heat conducting wall integral with the engine block. A second cooling liquid (e.g. water) is circulated through a cooling water passage adjacent to the heat conducting wall to remove heat from the first cooling liquid. It may also be pumped through other passages within the engine block for cooling purposes.
U.S. Pat. No. 4,674,449, which issued to Hundertmark on Jun. 23, 1987, discloses a pressure regulated cooling system. The cooling system for the engine of an outboard motor uses a pressure relief valve to control the coolant pressure and flow through the cylinder block. The relief valve member controls flow at the outlet of the block and is controlled by a diaphragm responding to pump discharge pressure at the inlet of the block. An orifice bypasses flow around the block when the main valve seat is closed and is closed by the valve member when the main valve seat is fully opened.
Some four cycle outboards exhibit a problem with regard to fuel dilution of oil when the engine is used in cold water. When lubricating oil is diluted with fuel, it does not offer the degree of lubrication that undiluted oil does. This can lead to accelerated wear of various moving parts of the engine. When an engine block is operating at relatively cold temperatures, the problem of fuel dilution is increased significantly. It would therefore be beneficial if a cooling system for a marine engine could be developed in which the cylinder block is prevented from operating for significant periods of time at temperatures that are below a desirable threshold.
The patents described above are hereby expressly incorporated by reference in the description of the present invention.
A cooling system for a marine propulsion device, made in accordance with the preferred embodiment of the present invention, comprises a water pump for drawing water from a body of water in which the marine propulsion device is operated, an engine having a cylinder head, a cylinder block, and an exhaust conduit connected in fluid communication with the engine to conduct exhaust gases away from the engine. It further comprises a first cooling passage disposed in thermal communication with the cylinder head, a second cooling passage disposed in thermal communication with the exhaust conduit, and a third cooling passage disposed in thermal communication with the cylinder block.
The first, second, and third cooling passages are connected in series fluid communication with each other. An outlet of the water pump is connected in fluid communication with the first, second, and third cooling passages in order to induce the cooling water to flow in a serial path through the first, second, and third cooling passages.
In a preferred embodiment of the present invention, the first and second cooling passages are connected between the water pump and the third cooling passage. The first cooling passage is connected between the water pump and the second cooling passage.
An inlet of the first cooling passage is disposed below an outlet of the first cooling passage. An inlet of the second cooling passage is disposed above the outlet of the second cooling passage. An inlet of the third cooling passage is is disposed below an outlet of the third cooling passage. The outlet of the third cooling passage is configured to return the cooling water to the body of water from which it was drawn by the water pump.
A charge air cooler is provided in certain embodiments of the present invention. The charge air cooler has a fourth cooling passage which has an inlet connected to the outlet of the water pump. An oil cooler has a fifth cooling passage with an inlet of the fifth cooling passage being connected to an outlet of the fourth cooling passage. As a result, water flows in a serial path through the fourth and fifth cooling passages. The first, second, and third cooling passages are disposed in parallel fluid communication with the fourth and fifth cooling passages.
Although the present invention, in a particularly preferred embodiment, connects the first and second cooling passages in series with each other, it should be understood that in other embodiments, only one of the first and second cooling passages may be connected to the third cooling passage. In alternative embodiments of the present invention, the first and second cooling passages can be connected in series with a third cooling passage, the first cooling passage can be connected in serial fluid communication with the third cooling passage, or the second cooling passage can be connected in serial fluid communication with the third cooling passage. In other words, the primary benefit of the present invention is that the cooling water is preheated by passing through either the first or second cooling passages, or both, prior to flowing through the third cooling passage. This heats the cooling water prior to it passing in thermal communication with the cylinder block.